South Africa's biggest trade union called on President Jacob Zuma to quit on Tuesday, in the wake of a cabinet reshuffle that has cost the country one investment-grade rating and deepened a rift within the ruling African National Congress (ANC).

Axar.az reports that Zuma's sacking of respected finance minister Pravin Gordhan in the reshuffle last Thursday has outraged his opponents and even some of his allies, undermining his authority as president and threatening to split the ANC, which has governed South Africa since the end of apartheid in 1994.

The rand, which fell as much as 1.9 percent at the start of trading on Tuesday, turned 1 percent firmer through the day as calls for Zuma to quit came in from unions, religious leaders, civil society and the opposition - although one analyst said he retained strong support within the party.

The ANC said late on Tuesday that it will brief media on Wednesday on decisions taken by its senior officials after two days of meetings over the fallout from Zuma's cabinet changes.

Cosatu, the biggest union and an ally of the ANC, joined the chorus of criticism, saying it no longer believed in Zuma's ability to lead, and that it wanted to restructure its alliance with the party.

"The time has arrived for him to step down and allow the country to be led forward by a new collective at a government level," Cosatu said in a statement.

It later said it would meet Zuma "as soon as possible" at his request to discuss the cabinet reshuffle.

Zuma himself, in his first public comments since he fired the internationally respected Gordhan, said that fiscal policies would be unchanged and that people should remain calm.

Rating agency S&P Global Ratings cited Gordhan's dismissal as one reason for its downgrade of South Africa to "junk" in an unscheduled review on Monday.